Solving coupled differential equations and Algebraic equation in MATLAB

I want to solve a system of 7 coupled differential equations and 1 algebraic equation in MATLAB with the method of lines. I could do it for each independent equation with some assumptions, but I can't solve these 8 equation together. Can you help me?

• Welcome to SciComp.SE. You are not providing enough information for people to help you. You can add the system of equations of interest for a starter. Sep 18, 2015 at 15:51
• Also, please try to write posts with good spelling and grammar. Sep 18, 2015 at 15:52
• Also, you could provide context and motivation. Are you going to spend \$100 of your own money building a balsa-wood bridge using this, or are you asking folks to do your homework? What kind of answer is going to be most valuable - one that "cuts to the chase" or one that "gives step by step" so you can generalize the approach? Sep 18, 2015 at 22:35

1 Answer

What you describe is called Differential-Algebraic Equation (DAE) system. Depending on the index of the system, these can be easy to solve or very hard. Take a look at: http://www.mathworks.com/matlabcentral/fileexchange/7481-manuscript-of--solving-index-1-daes-in-matlab-and-simulink-

Solvers ode15s and ode23t of Matlab can handle index-1 DAEs. If the system is stiff, ode15s is more suitable.

If you are interested in the theory behind them, or what is index and stiff, take a look at: http://www.scholarpedia.org/article/Differential-algebraic_equations

Edit: I didn't realize the OP was asking specifically for the method of lines. There is a section about DAEs here: http://www.scholarpedia.org/article/Method_of_lines

• Thanks a lot. I used this method for solving equations but now i have a problem for Function definition. I dont know how definite 7 coupled equations in one function. Can you help me? Oct 3, 2015 at 13:36